Process of purifying cellulose esters.



We terns Arnr rricnt BASIL W. BOESOI-I, OF BOSTON, MASSACHUSETTS.

PROCESS OF PURIFYING CELLULOSE ESTERS.

SPECIFICATION forming part of Letters Patent No. 708,457, dated September 2, 1902.

Application filed June 29, 1901. Serial No. 66,605. (No specimens.)

To wZZ whom it may concern.-

Be it known that I, BAsIL W. BOESOH, of Boston, in the county of Suffolk and State of Massachusetts, have invented an Improvement in the Purification of Cellulose Esters, of which the following is a specification.

All of the methods known to me for the manufacture of cellulose esters-as, for example, cellulose acetateinvolve the employment of a considerable excess of one or more of the reagentsas,for example,acetic anhydride or acetyl chlorid-in processes for the man ufacture of cellulose acetate. These processes are often further complicated by the presence of diluents or restraining agents, as nitrobenzol, chloroform, due. The necessity of removing this excess of reagents and of freeing the acetate from these diluents greatly complicates the preparation of the pure ester-as, for example, cellulose acetate. A common method of purifying cellulose acetate is by precipitating the acetate by alcohol from its solution in nitrobenzol, chloroform, or acetone, in which solution the excess of reagents is commonly carried. This method is expensive by reason of the great cost of alcohol, and is further complicated by the tendency of the alcohol to react with the esterizing agent, as acetyl chlorid and acetic anhydride with formation of an ester, as acetic ether. Similar difficulties generally exist in case of the formation of cellulose esters by methods involving the use of the anhydrides or chlorids of the appropriate acid radicals. I have discovered that this heavy expense may be materially re duced and the difficulties arising from the esterification of the precipitant or contamination of the product with the solvents-as, for example, in the case of nitrobenzol or chloroform-may be avoided by the use of a neutral-hydrocarbon, or mixtures of such hydrocarbons, as naphtha or similar light petroleum products, or benzol, as the agent for precipitating the esters and washing away the excess of solvents or reagents. I find that these neutral hydrocarbons are perfect solvents for acetic anhydride, acetyl chlorid, chloroform, and nitrobenzol, or a mixture of them,as well as for acetic acid in presence of the above reagents which are associated with the cellulose ester after its formation, and that by washing the acetate or other ester -with naphtha, benzol, or other neutral hydrocarbons or mixtures of them the acetate or other ester of cellulose, because of its insolubility in the hydrocarbon, is precipitated and may be entirely freed from the reagents. The washing may be carried out by any wellknown or suitable method. These neutral hydrocarbons, like naphtha and other light petroleum products, benzol, 850., have the merit of cheapness and of being substantially inert and neutral toward nitrobenzol and similar solvents of the esters and toward the anhydrides and chlorids or mixtures of them used in esterification. I prefer to use the petroleum products having a boilingpoint between 50 and 150 centigrade, the selection of the particular product to be used depending upon the boiling-points of the reagents and solvents to be removed, since by selecting the neutral hydrocarbons with proper reference as to its boiling-point, and

those of the several constituents of the mixture to be washed out, the subsequent separation and recovery of the reagents or solvents from the hydrocarbon by fractional distillation may be greatly facilitated.

I claim- 1. The method of purifying cellulose acetate, which consists in removing the excess of reagents by treatment with naphtha, substantially as described.

2. The method of purifying cellulose acetate, which consists in dissolving out any excess of acetic anhydride in naphtha, substantially as described.

3. The method of purifying cellulose acetate with recovery of excess of reagents, which consists in Washing out the excess of reagents by treatment with naphtha, and recovery of the reagents from the naphtha, by fractional distillation, substantially as described.

In testimony whereof I have signed my name to this specification in the presence of two subscribing witnesses.

BASIL W. BOESOH.

Witnesses:

B. J. NoYEs, JOHN W. DEoRow. 

